Endoscopes are used to view cavities in the human or animal body and also in technical objects. An endoscope typically comprises an elongate endoscope shank, which is suitable for insertion into the cavity to be viewed, and a head that can have attachments and control elements and also an eyepiece lens. Inside the endoscope shank and the head there is an optical system for transmitting an endoscopic image from the distal end of the endoscope, i.e. the end remote from the observer, to the proximal end, i.e. the end near the observer. For this purpose, the optical system comprises in particular a distally arranged objective for receiving the endoscopic image, an image carrier, and an eyepiece arranged at the proximal end of the endoscope, with an eyepiece lens for viewing the transmitted endoscopic image. The endoscope can be designed in particular as a rigid endoscope with a rigid endoscope shank and can have, as its image carrier, an arrangement of rod lenses accommodated in an optics tube arranged inside the endoscope. Moreover, the endoscope can have an illuminating device for illuminating the cavity to be viewed, and, if appropriate, it can have further devices, such as channels for endoscopic work instruments.
When assembling the optical components in the optics tube of a rigid endoscope, they are usually pushed into the optics tube from the proximal side in the sequence and arrangement predefined by the calculation of the optical system. In particular, the objective and one or more rod lenses, as well as, optionally one or more aperture stops and/or spacers are pushed in succession into the optics tube. For this purpose, the optical components have an external diameter that is slightly smaller than the internal diameter of the optics tube. With the aid of a system spring and a system closure guide, the entire optical system is pretensioned in the distal direction and thereby held against a distal closure piece of the optics tube, which can be provided in particular by a cover glass. What this achieves is that the optical elements, in particular the rod lenses, are assembled in a simple manner at the predetermined axial position thereof in the optics tube and can be removed again during a repair.
During use, endoscopes are exposed to significant mechanical loads, in particular accelerations or tremors and bending. Here, the optical elements are kept in the longitudinal direction at their respective predetermined positions by the pretension exerted by the system spring. However, as a result of the slightly smaller diameter thereof, the optical elements can move in the transverse direction in relation to the optics tube. In particular, the rod lenses can move with respect to one another and in relation to the optics tube in the transverse direction and can be tilted with respect to one another and in relation to the optics tube, as a result of which the optical axes of the rod lenses are no longer exactly flush with one another. Furthermore, the rod lenses can rotate about the longitudinal axis thereof, which can likewise lead to a deterioration in the imaging quality due to manufacturing-related tolerances, which the rod lenses are subject to.
The patent application DE 10 2013 101 650.2, which does not have a prior publication date, discloses the practice of fixing a rod lens received in the inside of an optics tube of an endoscope with the aid of a sleeve which can be welded to a desired position within the optics tube. The sleeve may comprise a ferromagnetic material. This enables a particularly simple handling when positioning the rod lens within the optics tube by virtue of the sleeve being pressed against the internal side of the optics tube by a magnet arranged outside of the optics tube and thereupon being welded to the optics tube in the position defined hereby.